Endocytosis and autophagy represent fundamental processes that are essential to the health of many cell types, including hepatocytes. Previous studies from our groups and others have identified cross-talk between endocytosis and autophagy: 1) specific compartments are shared between them; 2) both contribute to cellular proteolysis and 3) both pathways require regulated trafficking of vesicles that interact in a dynamic manner, undergoing fission and fusion as part of their maturation process. Based on prior findings, we propose that dysfunction of the endocytic or autophagic trafficking pathways can have deleterious effects on normal liver function and contribute to the pathogenesis of hepatic disorders. The overall goal of this proposal is to characterize at the molecular level the functional interaction between the endocytic and the autophagic pathways and their contribution to cellular homeostasis. To this end we will: 1) mechanistically define vesicle- associated protein complexes that regulate motor recruitment and activity required for endocytic/autophagic vesicle processing by fission and fusion; 2) determine the consequences of changes in membrane lipid composition on the interactions between endocytic and autophagic pathways and 3) characterize quantitatively the functional interplay between endocytosis and autophagy. We will use chemical and genetic manipulations in cultured hepatocyte cell lines and in rat and mouse liver combined with biochemical and morphological approaches to answer these questions. The complementary expertise of the two co-PIs, Dr. Allan Wolkoff (endocytosis and liver pathophysiology) and Dr. Ana Maria Cuervo (autophagy and cell biology) greatly enhances their ability to discover interactions between the endocytic and the autophagic pathways in liver and to study the consequences that failure in one of these pathways has on the other. The major significance of the proposed studies resides in the fact that alterations in endocytosis and autophagy have been observed in human diseases that include protein conformational disorders (e.g. alpha1-antitrypsin deficiency), cancer, metabolic disorders (e.g. diabetes, obesity) and infectious and immune diseases. However, incomplete knowledge regarding details of endocytosis and autophagy limits development of mechanism-based therapeutics. Successful completion of these studies will ultimately provide the tools needed to identify novel therapeutic targets to restore normal liver function or perhaps slow the functional decline associated with common liver disorders resulting from dysfunction of the endosome/lysosome system.